Preparation Of Cobalt-iron Based Catalysts And Electrocatalytic Oxygen Evolution Performance

At present,with the increasing global demand for energy,clean and renewable hydrogen is considered to be one of the most basic energy carriers to replace traditional fossil fuels and solve the energy crisis.Therefore,how to massively manufacture hydrogen in an environmentally friendly form is an extremely pressing issue that needs to be solved.Among the various hydrogen production technologies,the electrocatalytic water splitting hydrogen production technology has attracted widespread attention because of its advantages of cleanness,no pollution,and high efficiency.However,the water decomposition efficiency is largely limited due to the kinetic process of anodic oxygen evolution reaction is relatively slow in the conventional electrocatalytic water decomposition process.Therefore,the development of efficient,abundant,and economical oxygen evolution reaction catalysts is one of the main topics of current research.Among the various oxygen evolution catalysts,layered double hydroxides(LDHs)have been extensively studied in electrocatalysis because of their inexpensive price,unique layered structure,and chemical versatility.However,it still has some problems in practical applications,for example,the thick bulk form,poor intrinsic activity of the active site and the limited number of active sites.In the response to the problems above,in this paper,the CoFe sulfides(S-CoFe LDHs)are prepared by vulcanizing CoFe layered double hydroxides to improve the oxygen evolution activity of electrocatalysts.In addition,a third metal Ni ion is introduced into the LDHs to form NiCoFe layered ternary hydroxides(NiCoFe LTHs),which is used as a precursor.Then through vulcanization and acid etching(NiCoFe-S and E-NiCoFe)to improve the electrocatalytic performance of the precursor.The main research contents of this paper is as follows:(1)Firstly,the CoFe layered double hydroxides(CoFe LDHs)was synthesized by one-step hydrothermal method,then the thioacetamide was used as S dopantandvulcanized CoFe LDHs to synthesize S-CoFe LDHs catalyst.Compared with CoFe LDHs,S-CoFe LDHs catalyst shows better oxygen evolution performance and stability with a low overpotential of 300 m V required to achieve a current density of 10 m A·cm-2 in 1.0 mol·L-1 KOH solution,and it has a small charge transfer resistance.The reason is that the incorporation of S element changes the structure of the catalyst and improves the conductivity of the catalyst.The simple synthetic method greatly simplifies the material preparation process without multi-step reaction.(2)A suitable three-dimensional hierarchical structure can increase the surface area of the electrode and maximize the exposure of the catalytically active sites.In this paper,NiCoFe layered ternary hydroxide was used as a precursor,and NiCoFe-S electrocatalyst was successfully synthesized by vulcanization.The catalyst exhibits high oxygen evolution activity and good stability with a low overpotential of 200 mV required to achieve a current density of 10 m A·cm-2 and a small Tafel slope of 46.3 mV·dec-1 under alkaline condition for OER.NiCoFe-S exhibits excellent oxygen evolution properties,which can be attributed to the following.The incorporation of S element exposes the catalyst to more active sites and changes the valence state of each metal ion in the system,the redox properties of metal ions can provide significant electrochemical performance.(3)The precursor NiCoFe LTHs was etched with different concentrations of nitric acid to obtain an E-NiCoFe catalyst,and the experimental operation can be carried out at normal temperature.The structure of the material has changed after acid etching,and there are metal vacancies and oxygen vacancies in the system due to the acid-base reaction,so that the catalyst has excellent catalytic activity.For the above reasons,the E-NiCoFe catalyst exhibits excellent oxygen evolution activity and good stability with a low overpotential of 184 mV required to achieve a current density of 10 m A·cm-2 and a small Tafel slope of 37.8 mV·dec-1 under alkaline condition.